thompson



{No Model.) 6 Sheets-Sheet 1.

W. THOMPSON.

MANUFACTURE 0? WHITE LEAD.

No. 250,605. atented Dee. 6,1881.

1110' m k y' (No Model., 6 Sheets-Sheet 3.

W. THOMPSON.

MANUFACTURE OF WHITE LEAD.

No. 250,605. Patented Dec. 6,1881.

g Ill/l2 I J 4 17' (No Model) 6 Sheets-Sheet 4. W. THOMPSON.

MANUFACTURE OF WHITE LEAD.

Patented Dec. 6,1881.

6 Sheets-Sheet 6.

(No Model.)

W. THOMPSON. MANUFACTURE OF WHITE LEAD.

Patented Dec. 6,1881.

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N. PEYEns. PVIOKo-Lllhngmp UNrrnn STATES PATENT Farce.

MANUFACTURE OF WHITE LEAD.

SPECIFICATION forming part of Letters Patent No. 250,605, dated December 6, 1881.

Application filed August 15, 1881, (No model.) Patented in England October 6, 1880.

To all whom it may concem Be it known that I, WILLIAM THOMPSON, of Limehouse, in the county of Middlesex, England, have invented certain Improvements in the Manufacture of White Lead and in the Apparatus Employed Therefor, of which the following is a specification.

This invention has been patented to me by the Government of Great Britain by Letters Patent No. 4,056, dated October 6, 1880.

The present invention relates to improvements in the mode of manufacturing white lead in air-tight chambers, the object being to effect the conversion of metallic or blue lead into white lead of the best quality, both in respect to its color and body, in a speedy and economical manner.

It is well known that several processes are at present employed for the conversion ofmetal lic lead into white lead, and that in all these the same chemical elements are employed, but with very different results, both as respects the quality of the product and the cost of its pro ductiou.

The common process of obtaining white lead is that in which the metallic lead is subjected to the action of the heat and vapors arising from spent tanners bark and dilute acetic acid containedinvesselsembeddedinthebark. The process of conversion is very slow, extending over from three to five months, and when once started it is entirely beyond the control of the manufacturer. The percentage of corrosion, moreover, differs greatly from various causes, and it is seldom, if ever, that the whole of the metal is converted. \Vhite lead obtained by this method is liable to be discolored by the tan-vapors and requires to be carefully sorted, generally by hand labor, to remove the colored portions from the uncolored. Y

Attempts have been made from time to time to avoid the defects inseparable from the tanstack process by the use of an air-tight converting-chamber, into which the chemical'elements for corroding and convertingthe lead could be introduced and their supply controlled at pleasure, and these attempts have to some extent succeeded in removing certain difficulties which attended the stock mode of manufacture. One method which has been employed consists in subjecting metallic lead first to the action of steam and air, then to the action of aceticacid vapors, and subsequently tothe action of carbonic-acid gas, the three steps of this process being repeated as many times as are necessary to convert the metallic lead into white lead. Another method which has been proposed consists in mixing any one of several oxides of lead, litharge being preferred, with acetic acid to form a paste, which is subsequently exposed to the action of carbonic-acid gas; but this process is only applicable for convertin g oxide of lead and not metallic lead.

By the present invention I have succeeded in producing white lead of the best quality, the process being completely under the control of the manufacturer and insuring a larger yield than has heretofore been obtained from a given weight of blue lead, and also the entire conversion ofthe lead applied to the converting-chant her.

In carrying out my invention I use a converting-chamber similar to those heretofore employed, and, by preference, wheel carriages or trucks, on which the metallic lead to be converted into white lead is packed. I also employ open gutters or troughs in the floor of the chamber for receiving the dilute acetic acid, and steam-pipes, as formerly used, for vaporizing that liquid. I theu admit air and carbonic-acid gas to the chamber at a temperature which shall correspond with that of the chamber, and in such a manner as to prevent the formation of currents and eddies, which retard the chemical action of the gaseous elements, and I also provide increased facilities for controlling the heat of the chamber and the vaporization of the dilute acetic acid.

In the accompanying drawings, Figure 1 shows in transverse vertical section, and Fig. 2 in horizontal or sectional plan, an air-tight converting-chamber with an inner or supplementary roof, and with ends that open for admittin g the laden truck or wheel-carriage, and for discharging it after the process of conversion is complete, such chamber bein g also fitted with an arrangement of supply-pipes.

In these figures, A A is the closed converting-chamber, constructed of any suitable material. Bis a suspended or false roof, made of glass or equivalent material, and intended to receive and convey away the drops of condensed vapor falling from the roof, which condensed vapor might otherwise fall upon and waste or discolor the white lead produced. The chamber A extends upward at its apex into a longitudinal channel, 0, which is intended to receive the pendent pipes D, by which the air and carbonic-acid gas are admitted to the chamber. Of these pipes there may be any convenient number say three-and they are each fitted with branches D, which lead off to opposite sides of the chamber A, and connect with horizontal pipes D which are pierced with holes along their whole length. The pendent pipes D are furnished with hollow globes or chambers D of glass or other material, such as that used for the pipes and for the cooks with which the pipes are fitted, it being essential, as is well known to white-lead manufacturers, that the material usedfor such purposes within the chamber should be such as will resist the action of the acetic acid and other "apors. The object of the globes or chambers D is to destroy all tendency which the air or gas may have to rush into the chamber in direct currents, and also to present a heating-surface to the air or gas prior to its exitfrom the pipes into the chamber.

E is the carriage, formed with a series of shelves, on which are placed skeleton-frames E for receiving the metallic or blue lead that is to be converted into white lead. These frames E have a tray for their base to receive any droppings from the lead, and they are provided with horizontal bars or rails upon which rest lugs that project laterally from the castmetal plates of lead. These plates, which may be cast either solid or in the form of net or lattice work, I prefer to make of about an eighth of an inch thick, but any other determinate thickness of plate up to half an inch may be used, if thought desirable. These plates 1 insert in the frame transversely of the same and about an inch apart, increasing the space in proportion as the thickness of the plate is increased,in order to provide ample room for the swelling of the lead during the converting process. The carriage E is mounted upon flanged wheels, which run in grooves formed in the floor of the chamber and are continued beyond the opposite ends thereof.

F F are troughs formed in the floor of the chamber, and supplied with dilute acetic acid from a well, F.

G G are steam-pipes fitted in the troughs F, and serving to vaporize the dilute acid supplied to the troughs. G G are other and larger steam-pipes, which are intended to heat the chamber at the commencement of the operation, and to supply dry heat from time to time when the steam is cut off from the pipes G on the occurrence of too free an evolution of acid vapors. In order that the attendant-may readi- 1y ascertain the temperature of the chamber, suitable thermometers are provided, as shown at H H, Figs. 3 and 4. This double system of supplying heat to the chamber offers great facilities to the attendant, as he can regulate the heat of the chamber without unduly increasing or diminishing the temperature of the chamber or the amount of contained gas and vapors.

For the purpose of increasing or diminishing the supply of air or of carbonic-acid gas to the chamber, cocks are provided for cutting off at pleasure any one or more of the horizontal pierced pipes D which admit, (as will hereinafter be more fully explained,) first, air to the chamber, and then air and carbonic-acid gas combined.

1 will now describe my improved process of converting metallic lead into white lead.

The converting-chamber having been charged with the lead to be converted into white lead, (the same having been previously washed over with acetic acid or ammonia to clean its surface,) the troughs F are charged with acetous liquid, generally with acetic acid and water, (in the proportion of one of'acetic acid to twenty ot'water,orthereabout.) The converting-chamberis then closed. Steam is now passed through the pipes G and G to raise the temperature of the converting-chamber to from 80 to 120 Fahrenheit, or thereabout, and to commence the evaporation of the acetic compound contained in the troughs. When this temperature has been reachedin the converting-chamber atmospheric air from any convenient apparatus say, for example, a gas-holder--is supplied at a moderate pressure through the globes and pipes D D D D to the chamber, and diffused through the same with only a comparatively slight disturbance of the imprisoned atmosphere. The action of the air, and of the aceticaeid vapor thus supplied to the chamber, I m aintain without interruption for from three to four days and nights. During this period the metallic lead is attached and becomes covered with a whitish coating of hydrated suboxide and hydrated subacetate of lead, a mixture of these lead compounds being formed on the surface of the lead, The process I now continue with the addition of carbonic-acid gas, which gas may be generated in any convenient and economical manner. When purified, this gas is supplied to the chamber at a moderate pressure through the system of pipes and globes D D D D or any portion thereof, (together with a further supply of .air,) to accomplish the work of carbonating the compounds of lead already formed, and this supply of mixed gas and atmospheric air I maintain until, by inspecting suitably-arranged sight-holes, I ascertain that the conversion is completed or carried to the desired extent. The proportions ofatmospheric air and carbonic-acid gas admitted simultaneously through the same system of pipes to the chamber will be about equal in quantity. The

combined action of the acetous vapors, atmospheric air, and carbonic acid is kept up at a proper and regulated temperature (by preference slowly increasing from 80 until the maximum temperature of Fahrenheit is reached) for such a time as is sufficient to convent the metallic lead into white lead. The time necessary for the completion of the process of conversion will vary from twelve to twenty-eight days, according to the quality and thickness of the lead. With good soft lead one-eighth of an inch in thickness twelve days will usually suffice, and for the same lead onehalf an inch in thickness twenty-eight days will be sufficient time. I have found in practice that there are certain conditions of the metal while under conversion that favor the process, but there are others that do not. For instance, lead one-eighth of an inch in thickness, when treated with carbonic acid, aceticacid vapor, and air, after the formation of the hydrated suboxide and subacetate, becomes penetrated in parts and the coating of white lead falls off almost as soon as it is formed. WVith thicker metal the white lead,when formed on the surface of the blue lead, exfoliates from the surface of the metal, but does not fall away. It remains as a. porous coating, surrounding and partly attached to the remaining metallic core, by its presence greatly favoring the action of the process of conversion of the remaining metal, so that twenty-eight days will suftice for this thickness; but in some cases, as when the coating of converted lead from any cause, such as employing too great heat, gets hardened and loses to some extent its porosity, it then protects the core of lead from the action of the gases and vapors, and a longer time will be necessary for the complete conversion of the metal. Again, when too much acetic acid and too small an amount of carbonic acid is supplied to the chamber the coating is then to some extent soluble in the vapors,and, running over the lead, coats and protects it from proper continuous action. When the process of conversion is completed the steam-heat is turned off from the converting-chamber and the continuous supply of air and carbonic-acid gas is also stopped.

The apparatus employed in carrying out the above-described process may be modified to suit the varied requirements of the manufacturer.

Fig. 3 shows in cross section a chamber suited to receive two carriages charged with cast plates of lead, the two loads being simultaneously submitted to the process. In this form of chamber no inner or supplementary roof is required, the condensed vapors running down the inclines of the root to the center and falling into a gutter in the floor (between the carriages) provided to receive the droppings. This arrangement of the pipes and troughs will be substantially the same as in the first-described arrangement.

Fig. 4 is a cross-section, and Fig. 5 a plan view, of a chamber furnished with a modified arrangement of distributing-pipes. In this example the chamber has a door only at one end for the admission and withdrawal of the carriage or truck, and the heating-pipe G is arranged so as to extend along the two sides and ends of the chamber, it being necessary to dip the heating-pipe at the entrance end of the chamber to keep it clear of the carriage-way. The distributingpipes, instead of being within the chamber, as shown at Fig. 1, are set out side the chamber, and havejets or branches which enter the chamber at three different levels, and are furnished with globes D which serve to heat the air or gas admitted to them, and to diffuse the same gently throughout the chamber. 1

In all the arrangements of distributingpipe the cocks which control the delivery of the air and gas to the converting-chamber are made accessible to the attendant outside the chamber, as is clearly shown in the figures.

The atmospheric air and carbonic-acid gas may, if thought desirable, be warmed and brought to the same temperature as the atmos phere within the converting-chamber by any convenient means before admission to the distributing-pastes, and this will be found desirable when the arrangement described with reference to Figs. land 2 is employed. It is found that the combined action of the gases and vapors is more energetic when all are acting at the same temperature. When the conversion of the metallic leadinto white leadis complete I cool the converting-chamber and clear it of any residual gases and vapors by either blowing air through the converting-chamber, or by exhausting the air from the chamber at one part and allowing air to enter at another. The converting-chamber may then be opened and the contents removed without any injury or even inconvenience to those engaged in the manufacture. The'white lead produced is then prepared for the market in the usual manner.

It is to be observed that in my improved process of manufacturing white lead I not only produce a commercial article of absolute purity, but one which cannot be excelled, if equalled,

in density, in homogeneity,in opacity, or body power, when made into a paint, and this my improved process can be carried out on the largest or smallest scale, and that absolutely without any injury to those engaged in the manufacture.

To the convertingchamber I attach at some convenient place, generally to the upper part of the gas-space of the converting-chamber, a waste-box. A pipe from this box communicates with an adjacent chimney, and is used to conduct away any waste gases or vapors. This under ordinary circumstances is sufficient guard against the gases or vapors passing into the factory; but it is sometimes necessary to absorb these deleterious gases--as,for instance, when no furnace-shaft is available for receiving them. Under these conditions I arrange for the absorption of the waste deleterious gases or vapors in an apparatus arranged as shown in the sectional view, Fig. (i, and connected withtheconverting-chamber. This apparatus consists of a vessel or box of enameled metal or wood or other suitable material fitted with an inlet-pipe, by which it communicates with the converting-chamber, and also with an outlet-pipe. The vessel is provided with partitions reaching alternately from the inner top face nearly to the bottom and from the inner bottom face nearly to the top, by which means the waste gases and vapors passing through it are compelled to travel in a circuitous passage from the converting-chamber through the vessel, which I fill with coke or some porous substance which has been moistened with water or water rendered alkaline. On exhausting this vessel the waste gases and vapors will be drawn into the box and absorbed in their passage through the moistened porous material. A tap is provided for drawing off any liquid which collects at the bottom of the vessel, and the partitions attached to the bottom of the vessel are perforated to permit of the fluid matter collected from the surface of the coke freely passing to the tap. The vessel should also be provided with man-holes in each compartment for charging or emptying the vessel.

I am aware that it is old in ventilating apparatus to conduct or force air through acham her containing water or other absorbent to rid the air from particles of solid matter held in suspension and from gases deleterious to health and I am also aware that perforated pipes and similar distributing devices have been employed for supplying air to or exhausting air from dwellings, railway-cars, and other structures to be ventilated. I do not therefore claim the above as of my invention.

Having now set forth the nature of my invention of improvements in the manufacture of White lead and in the apparatus employed therefor, and having explained the manner of carrying the same into effect, I would have it understood that I do not claim, generally, the admission of a regulated supply of air and carbonic-acid gas to a confined atmosphere of acetic-acid vapor in which metallic lead is exposed to corrosion; but

What I claim as my invent-ion isl. The process of converting metallic or blue lead into white lead, as above described-that is to say, first submitting metallic lead in a closed cha mber to the combined action of aceticacid vapor and atmospheric air in a temperature ranging from 80 to 120 Fahrenheit, or thereabout, for one-sixth to one-fourth of the time required for completing the conversion of the lead, and subsequently supplying to the closed chamber, in addition to the acetic-acid vapor, carbonic-acid gas and atmospheric air and maintaining the supply until the conversion is completed, the admission of the air and gas being so controlled as to provide for their diffusion through the chamber without the creation of disturbing currents.

2. In an apparatus for manufacturing white lead, the combination ofa converting-chamber, steam-pipes arranged therein for heating the same, globes or chambers arranged in said converting-chamber and adapted to be heated by the heat of said chamber, pipes for conducting carbonic-acid gas and air to said globes or chambers, and pipes, arranged substantially as described, for conducting the heated carbonic-acid gas and air and distributing them throughout the converting-chamber, all substantially as specified.

London, June 23, 1881.

\VILLIAM THOMPSON.

Witnesses:

H. K. WHITE, GEO. OANTLE,

Both of 66 Chancery Lane, London. 

